The requirements for fabric for firemen's coats and other protective clothing and devices are not only stringent but have never been completely met by commercially available trim products to date. The National Fire Protection Association (NFPA) Standard on Protective Clothing for Structural Fire Fighting specifies that: (1) the outer shell material of protective clothing for fire fighting shall not char, separate, or melt when placed in a forced air laboratory oven at a temperature of 500.degree. F. (260.degree. C.) for a period of five minutes; (2) firemen's coats shall be trimmed with at least 325 square inches (0.21 m.sup.2) of retroreflective fluorescent tape in a configuration which includes at least tape around each sleeve and a band around the bottom of the coat near the hem; and (3) the use of fluorescent retroreflective trim material is an important safety feature for fire fighter's outer wear, important characteristics of such trim being shrinkage with temperature, the temperature at which the material will char or melt and drip, and the effects of temperature exposure in a forced air oven.
A commonly used trim for firemen's coats comprises a plastic sheet material having cube corner optical elements for retroreflectivity which sheet material is bonded to a fabric scrim in such a way as to provide rectangular cells which provide the air interface at the tetrahedra of the cube corners needed for reflectivity. Although this type of trim is glossy, retroreflective and easily cleaned, it suffers significant (80%) loss of reflectivity at 300.degree. F. (149.degree. C.), 100% reflectivity loss at 350.degree. F. (177.degree. C.) and is virtually destroyed at 450.degree. to 500.degree. F. (232.degree.-260.degree. C.).
The use of retroreflective markings on various articles of clothing is well known in the art, see U.S. Pat. Nos. 2,567,233 and 3,172,942. The retroreflective sheet material of U.S. Pat. No. 2,567,233 provides a flexible weather resistant sheet comprising a light-reflective binder coating in which is partially embedded a firmly but resiliently bonded surface layer of small, transparent, convex lens elements such as glass beads or microspheres, preferably having a refractive index of about 1.7 to 1.9 and a diameter of less than about 10 mils (250 micrometers). Bead diameter is typically about 40 to 150 micrometers. The binder is typically a rubbery polymer such as butadiene-acrylonitrile copolymer containing a reflective pigment such as aluminum flakes as well as resin and a plasticizer. Such retroreflective sheeting may be provided with a heat activated or solvent activated adhesive on the side opposite the glass beads and thereby be bonded to garments or fabric.
Retroreflective sheeting may have a reflective (e.g. aluminum) coating placed on the backs of or behind the glass beads, rather than being provided by loading the binder layer with aluminum flakes or particles. The manufacture of retroreflective sheeting products is described in U.S. Pat. No. 2,567,233 at columns 3-5 and U.S. Pat. No. 3,172,942 at columns 4-7.
Alternatively, the reflective means may comprise a series of transparent dielectrics (i.e. a dielectric reflector), each having a thickness which is an odd numbered multiple of about one-fourth of the wavelength of light in the wavelength range of about 3,800 to 10,000 angstroms, as described in U.S. Pat. No. 3,700,305. The refractive index of each transparent dielectric layer must be at least 0.1 (preferably at least 0.3) higher or lower than that of the adjacent layers.
There are several other varieties of retroreflective sheeting besides the exposed lens variety (i.e. glass beads exposed to air) described above: enclosed lens sheeting having a transparent layer covering the outer surface of the glass beads; encapsulated lens sheeting having a transparent polymeric layer over the front of the glass microspheres and bonded in such a way as to result in air cells infront of the microspheres; and cube corner reflective sheeting which uses tetrahedra or other prismatic corner shapes as the lens elements instead of glass microspheres.
For purposes of this discussion, the lens elements may mean either cube corner reflectors or glass or glass-like beads or microspheres. Also, the term retroreflective sheeting as used herein may mean any of the above-described types of sheeting.
The patents referred to above dealing with retroreflective sheeting do not propose its use in fire fighter's garments and they are not designed to pass the rigid tests previously mentioned. Indeed, most would burn, char, melt or drip upon exposure to fire or in an oven at 260.degree. C. for ten minutes.
It is the object of this invention to produce a trim which is useful for fire fighters' garments which is: flame retardant, resistant to melting, charring or dimensional change in a 500.degree. F. (260.degree. C.) air circulating oven for five minutes, highly retroreflective, fluorescent and resistant to dirt and soot accumulation and/or easily cleaned.